The IEA's annual World Energy Outlook, released today, looks at what would be required to keep global warming below 3.6°F (2°C), a threshold many countries have pledged to stay below.

"We're increasingly pessimistic," said Richard Jones, deputy executive director of the IEA and a former U.S. diplomat.

"We've been trying to warn our member countries," which includes most of the industrialized world, Jones said. "It's getting harder and harder to meet this target."

To have a good chance of staying below that amount of warming, the world has only a certain budget of emissions it can use—the equivalent of about 1 trillion tons of carbon dioxide emissions by mid-century.

The infrastructure the world is building today—including power plants, buildings, and factories—is based largely on burning fossil fuels, the main contributor to emissions of carbon dioxide (CO2), the primary greenhouse gas, the report noted.

Once built, infrastructure usually stays in place until it wears out—so what we build now will "lock in" emissions for decades to come, the IEA argues.

The infrastructure already built today or in the planning stages would, over the coming decades, emit 80 percent of all the CO2 the world can afford to release into the air.

To keep emissions below that target, civilization could continue with business as usual for only five more years before the total allowed budget of emissions would be "locked in." In that case, to meet the targets for warming, all new infrastructure built from 2017 onward would have to be completely emissions-free.

"We can still act in time to preserve a plausible path to a sustainable energy future," said IEA Executive Director Maria van der Hoeven. However, she added, "Each year the necessary measures get progressively tougher and viciously more expensive."

False Economy

The report's conclusion is "a pretty stark message," Jones said. "The key thing is to get policies in place by 2017" for a massive switch to low-carbon infrastructure.

That's because longer delays would mean that more infrastructure would have to go "out to pasture," or be retired before its normal lifetime was up, he added.

And retiring infrastructure early would mean that avoiding dangerous climate change would cost much more money.

For that reason, the report argues, "Delaying action is a false economy."

"We estimate that for every dollar you don't spend today" on low-emissions infrastructure, Jones said, "in the future you have to spend four."

Because of this high cost of later action, the report said, meeting the climate target would be "much more difficult and expensive, or even, in terms of practical politics, impossible."

To achieve these targets, more than half of all new energy sources installed from now on would have to be renewables such as solar and wind, the IEA forecasts. To ramp up renewables that quickly would require large subsidies, rising on a fast pace to reach $250 billion a year by 2035—four times today's level.

Even at that level, those subsidies would be less than half as much as the world spends now on fossil fuel subsidies, according to IEA estimates.

Meeting the targets would require increasing nuclear power as well. So far, Japan's Fukushima disaster has damped enthusiasm for nuclear power in Europe, but elsewhere has had very little impact, with Russia, China, India, and other countries still planning large growth of nuclear power, the report said.

The climate targets would also require growing use of natural gas in place of coal—but the IEA has argued that this would be possible, because new technologies such as hydraulic fracturing have dramatically increased recoverable supplies.

Room to Maneuver

Because of the lock-in from infrastructure, meeting the climate target is a tall order, said Richard Newell, an energy economist at Duke University and former director of the U.S. Energy Information Administration.

"Even if it were technically possible, it is not economically or politically realistic," Newell said.

"Unless something significant changes about our energy technologies, markets, and policies," he added, "current trends lead to an energy future that looks very much like the present. Just bigger-much bigger."

The IEA's analysis comes to a very similar conclusion as other studies, including one published last year in Science.

"It is clear that the energy infrastructure already in existence doesn't leave us with much room to maneuver under current climate benchmarks," said Steven Davis, a climate researcher at Carnegie Institution for Science in Stanford, California, and lead author of the earlier study.

"The transition to energy infrastructure that doesn't emit CO2 to the atmosphere will take time, something that is in short supply."